1. Field of the Invention
The present invention relates to: an imaging system capable of capturing a 360-degree field of view image in a single shooting; software used for controlling data representing the captured image; a method for correcting distortion in an image captured by the imaging system; and a recording medium storing procedures for such a method. From the image captured by the imaging system, space geometry, a configuration of an object, etc., can be correctly perceived. Such an imaging system can be preferably used in wide-ranging fields including the field of security for monitoring stores, banks, etc.; the field of on-vehicle use, such as avoidance of automobile collision, and monitoring of the inside of a vehicle; and the field of measuring instruments for use in a visual section of an industrial robot, for example.
2. Description of the Related Art
In a conventional imaging system capable of capturing a 360-degree field of view image using a hyperboloidal mirror, a reflecting mirror having a geometry of one of two sheets of a two-sheeted hyperboloid (hereinafter, referred to as “the first sheet of a two-sheeted hyperboloid”) is used as the hyperboloidal mirror for producing a central projection image. A lens center of a camera is arranged in a focal position of a geometry of the other one of the two sheets of the two-sheeted hyperboloid (hereinafter, referred to as “the second sheet of a two-sheeted hyperboloid”) opposed to the first sheet of the two-sheeted hyperboloid (see, for example, Japanese Laid-Open Patent Publication No. 6-295333).
FIG. 2 is a diagram for explaining a two-sheeted hyperboloidal function and its characteristics.
In the imaging system which uses a hyperboloidal mirror having a geometry of the first sheet of a two-sheeted hyperboloid (shown at the top in FIG. 2), where a lens center of a camera is arranged in a position of focus O2 of the second sheet of the two-sheeted hyperboloid (shown at the bottom in FIG. 2), when an object is input (captured) as an image, the input image (captured image) is a central projection image. A positional relationship between the central projection image and the object can be represented by the following
Expressions (1) and (2):
                              x          =                                    F              ×                              (                                                      b                    2                                    -                                      c                    2                                                  )                            ×              X                                                                        (                                                            b                      2                                        +                                          c                      2                                                        )                                ×                                  (                                      Z                    -                    c                                    )                                            -                              2                ×                b                ×                c                ×                                                                            X                      2                                        +                                          Y                      2                                        +                                                                  (                                                  Z                          -                          c                                                )                                            2                                                                                                          ;                            (        1        )                                y        =                                            F              ×                              (                                                      b                    2                                    -                                      c                    2                                                  )                            ×              Y                                                                        (                                                            b                      2                                        +                                          c                      2                                                        )                                ×                                  (                                      Z                    -                    c                                    )                                            -                              2                ×                b                ×                c                ×                                                                            X                      2                                        +                                          Y                      2                                        +                                                                  (                                                  Z                          -                          c                                                )                                            2                                                                                                    .                                    (        2        )            
One of advantages of the imaging system using such a hyperboloidal mirror is that the central projection image can be readily transformed into an image in any spatial position around the central projection image.
However, in the conventional imaging system using the hyperboloidal mirror, the lens position for producing the central projection image is limited to one point (focus O2). Thus, it is difficult to align a lens with a position which is optimum for installing the lens.
Moreover, in this lens position (focus O2), in view of performance of the lens, it is not easy to focus the lens on an entire surface of the hyperboloidal mirror for the purpose of capturing an image reflected in the hyperboloidal mirror, since a minimum distance from the lens to a virtual image (an object reflected in the hyperboloidal mirror) formed in the hyperboloidal mirror (a distance between a vertex of the hyperboloidal mirror and the lens) is short. As a result, the central projection image is captured by the conventional imaging system under a condition where the focus is not adjusted to be on the entire surface of the hyperboloidal mirror, rather the focus is adjusted to be only on a partial area of the surface of the hyperboloidal mirror. The area of the surface of the hyperboloidal mirror on which the lens is focused has, for example, a doughnut-shape, and as such the entire central projection image is not captured.